I've often heard 1/effective focal length, and that seems to match what you're saying. For DSLR crop sensor formats (1.5, 1.6, 1.7 crops) the math is a bit harder but the rule is easy to remember.

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OM-D E-M5 || O12-50 | P45-175 | P100-300 | PL25 | O45
Adapted: Minolta MD 28/2.8 Celtic, MD 35/1.8, MD 50/1.4, MD 85/2.0, MD 200/2.8, Nikon 100/2.8 E
Wish List: GH3, 12/2.0, 17/1.8, 75/1.8, Oly ZD FT SHG 300/2.8
Pentax K-5, K-01 || 18-135 WR | Sigma 30/1.4

Just for laughs, I mounted my Canon EF 70-200/2.8 on my E-M5 - the IBIS works wonders to stabilize the image handheld. Didn't peep at the pictures, as manually focusing a lens I can't stop down is a bit of a pain. Still, I'll pop the 100-400 on there just for the sake of hilarity at some point.

(I mostly got the EF adapter because several of my legacy lenses have EF adaptors on them I'd rather not be swapping around all the time, but I figured I'd pop one of the biggest bits of glass I own on there just to entertain myself)

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EOS: 5DII, 30DIR, 24-105L, 35L, 135L, 15/2.8 FE, Σ 50/1.4, Σ 105/2.8 macro
Mu43: GF2, E-M5, P14/2.5, P20/1.7, O45/1.8, P7-14, O12-50, P12-35, P100-300
Legacy: Contax Zeiss 50/1.4, 35/2.8, Leica R 50/2.0, 28/2.8, Pentax 50/1.7

Yes, the same thing. I try not to think of "effective focal length". I've used 35mm, medium format and 4x5 over the years. So what's the "crop factor" when I want the same field of view as a 135mm on 4x5? I don't know and it doesn't matter to me. Basically I'm just trying to forget 35mm "full frame" and get used to 4/3.

Fred

So it sounds like we've got essentially the same results, we just need a bigger sample size to average out the data points.

Forgot to mention, I noticed that having both IS systems activated doesn't seem to make my pictures blurry, either. Strange, I think.

Id like to ask Amin and anyone else with relevant knowledge whether the ibis in the O - MD is significantly better than that of previous M4/3rds Olympus bodies as this does not seem to have been clarified ? Rob

I haven't done formal testing, but it seems more effective to me.

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Amin
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Anecdotally I'd say it is definitely better than the EP3. Viewfinder stabilization aside (a huge benefit over the EP3) I've noticed I can pull off some crazy low shutter speeds with the EM5 with my 100-300 with more regularity than I could with the EP3's IBIS or the lens' OIS.

The 9fps burst mode helps makes shooting marginal shutter speeds less of a chore, too. 3 frames go by in the blink of an eye.

All I know is that I can hand hold the camera with the PL25mm lens and the IBIS of the E-M5 lets me shoot a stationary object at shutter speeds as low as 1/3 second with sharp images, even at 100%. Which is pretty good.

None of my Panasonic lenses have image OIS, so I can't do any side by side test, but that's not the point, not to me anyway. The IBIS of the E-M5 does more than what I need it to do, and I'm getting way more keepers at 300mm bird shots. If the Panasonic OIS does the same thing, I think that's great. Never thought I had to hate Panasonic because I shoot Olympus cameras.

The who is better, King Kong or Godzilla, doesn't interest me enough to fight about it.

Oh, come on! It's so much fun to tell the other kids how awful their toys are! With the best toy you're king of the playground!

True. True. In the day, my toy trucks were all metal. I could do an old geezer (I'm old enough) "not all plastic like today!"

But alas, my all metal trucks are now all rust.